FI56541C - FRAMEWORK FOR FRAME STABILIZATION OF UREAFORMALDEHYDHARTSER - Google Patents

Description

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Patent application (45) ^ / 51) Kv.ik. * yint.a. * C 08 G 12/12 '' D 21 H 3/5 * FINLAND - FINLAND (21) Patent application - Patentansttltnlnj 1968/72 (22) HakemlspUvi - AnsSknlngsdag 11.07.72 (23) The beginning of the cloud - Giltlghetsdag 11.07.72 (41) Become public - Blivlt offentllg ^ 7.01.73

Patents and Registry Offices !! * / 44) Date of filing and registration. -

Patent- oeh registerstyrelien 'AnsBkan utlagd och utUkrlften publlcerad 31.10.79 (32) (33) (31) Pyydetty etuoikeus —Begird priorltet i6.07.71

Federal Republic of Germany-Förbundsrepubliken Tyskland (DE) P 2135738.0 (71) Badische Anilin- & Soda-Fabrik Aktiengesellschaft, Ludwigshafen,

Federal Republic of Germany-Förbundsrepubliken Tyskland (DE) (72) Friedrich Brunnmueller, Ludwigshafen, Helmut Henkel, Ludwigshafen,

Johann Lenz, Ludwigshafen, Federal Republic of Germany (DE) (7I +) Oy Kolster Ab (5 * 0 Method for the production of storage-resistant urea formaldehyde impregnating resins - Förfarande för framställning av lagerstabila urea-formaldehydharts

Urea formaldehyde condensate-based impregnating resins are known. They form the major part of amino-plastic binders in the finishing of wood and wood-based surfaces and in the corresponding fields of technology.

Amino resin impregnating resins are available in large quantities, are almost colorless, and can be processed into durables.

Since the properties of the cured binder can be influenced, for example, by various additives, the properties of the dissolved resins, which determine the processability of the actual impregnating resin solutions, are in need of continuous improvement.

In particular, a high saturation rate and good storage stability of the resins or their solutions are sought. However, experience has shown that improving one trait tends to degrade another trait. Experience has shown, for example, that the optimum impregnation capacity is achieved so that the impregnation solutions contain a large amount of small-molecule condensates. Such impregnating resin solutions are obtained mainly by condensation of alkaline or slightly acidic acid. In practice, however, they are not sufficiently storage-stable.

If the aminoplastic resin solutions are acidically condensed to such an extent that they become sufficiently storage-stable, these products are only of limited suitability as impregnating resins due to their high viscosity. Due to their high content of methylol compound, alkali-prepared resins have a good impregnation ability. However, the solubility of urea methylol compounds is rather low. Alkali-condensed impregnating resin solutions already become supersaturated at a resin concentration of U0-60% due to their methylol compound content, and after some time a solid bottom precipitate separates from them.

In particular, after the addition of emulsifiers, other polymer dispersions and curing agents, the reactions leading to the formation of the precipitate are often rapidly accelerated, i. the run-off time of the resins is considerably shortened. At the same time, the viscosity is constantly increasing so that when impregnating the paper, a so-called resin nests, i.e. the impregnating resin is unevenly distributed in the substrate. Namely, in order for the cellular cavities of the paper fibers to be well impregnated, it is necessary that the viscosity of the impregnating resin solution remain low for a long time.

Thus, the object is to prepare urea formaldehyde impregnating resins, the solutions of which penetrate rapidly into the fiber cavities without retaining the binder component on the surface of the fibers. In addition, the shelf life of the solutions must be good.

Although several proposals for improving these properties are still known today, based on the conversion of condensates with e.g. condensable additives, these are generally not economical because urea and formaldehyde are very cheap pulp products that can hardly be partially replaced without affecting economy.

It has been found that storage-stable, urea- and form-aldehyde condensate-based resins with excellent impregnation properties can be prepared by first preparing solutions of high molecular weight resins and post-treating them in a certain manner with formaldehyde.

The invention therefore relates to a process for the preparation of storage-resistant urea-formaldehyde impregnating resins, in particular for finishing wood surfaces, characterized in that a) urea and formaldehyde are condensed in a known aqueous solution in a molar ratio of 1: 1.5-1: 2.5 at least as far as cold; - a sample of the condensate solution dropped into the / S magnesium sulphate solution causes turbidity and up to the point where the resin of the solution remains dissolved above 60 ° C, h) at least 0,2 mol of formaldehyde per mol of urea are then added so that the molar ratio of urea to formaldehyde becomes 1: 2.5-1: ^ and condensed at a temperature between U0 ° C and the boiling point of the solution at pH 3 66541 3.5 ~ 9 until the resin solution remains clear at room temperature when diluted with at least twenty times the amount of water, and

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c) optionally then optionally adding urea to a total molar ratio of urea to formaldehyde of 1: 1.5-1: 2.5 and post-condensing at pH 1 +, 0-6.5 until free urea disappears.

It seems that the success of the measures according to the invention is explained by the fact that in this process the formation of small-molecule methylol compounds of urea is prevented, which leads to unstable, supersaturated solutions and the continuation of condensation.

The post-treatment ("condensation") described in b) with formaldehyde can be carried out in the pH range 3.5-9 · It is preferred to carry out the post-treatment in the pH range 1 +, 5-6.5. If the pH falls below l +, 5, resins which have already significantly deteriorated their saturation capacity are obtained empirically. Above pH 6.5, the curing rate of formaldehyde-treated resins has slowed upon condensation.

The post-treatment with formaldehyde can take place at a temperature between 1 + 0 ° C and the boiling point of the condensation solution, which is normally about 95 ° C.

However, it is advantageous to treat at a temperature of 60-95 ° C. At temperatures below 60 ° C, condensation solutions tend to cloud too early and especially if they contain a lot of high molecular weight material.

The molar ratio of urea to formaldehyde in the resins prepared according to a), which are intended for post-treatment with formaldehyde, is 1: 1.5 to 1: 2.5.

They are condensed in the usual way acidically, i. At pH values below 7, especially in the range U, 5 to 6.5 - The resin content of the solutions, which can be determined, for example, as dry matter, is generally 1 + 0-70 wt.

The resin solutions for the post-treatment of b) can be prepared immediately before treatment, using commercial resin solutions according to the invention or preparing and using resin solutions obtained by dissolving a commercially suitable resin powder without departing from the invention.

Prior to post-treatment with formaldehyde, the condensation of the resins according to the invention must continue to such an extent that a slight clouding occurs when adding a drop of resin solution to a cold, 50- $ magnesium sulphate solution (Mg 3 O 2 + 2 ° C), e.g. However, the degree of condensation must not be so high that the undiluted resin solution begins to cloud or form two phases already above 60 ° C, as it is difficult to remove the fines already formed by adding formaldehyde. The latter characteristic of the resin solution space is, of course, not only a measure of the degree of condensation, but also an indication of the chemical structure of the condensates. However, the complex and still little-known method of condensation of many formaldehyde resins is well reproducible and thoroughly described in these samples, so that the method is familiar and easy to implement for any person skilled in the art. The relationship between the durability, water resistance, temperature and degree of condensation of saline solutions is shown in the practical test series below.

The amount of formaldehyde required in post-treatment to convert high molecular weight resins to storage-stable, low-viscosity and highly saturable resins depends largely on the degree of condensation of the resins being treated. It is higher the further the resins have been precondensed before treatment, i.e. as expressed in the previously described method for determining the degree of condensation: the lower the salinity and water resistance of the resins used. However, the amount of formaldehyde in the post-treatment must be dimensioned so that the total ratio of urea to formaldehyde, based on the amount of post-treatment resin and formaldehyde added, is 1: 2.5 to Is4 and at least 0.2 moles of formaldehyde are added per mole of urea. Most preferably 50-50 5% aqueous formaldehyde solution is used. In many cases, formaldehyde-rich pre-condensates of urea and formaldehyde with a molar ratio of urea to formaldehyde of more than 1: 5 can be used as the formaldehyde donor. The resins obtained from the post-treatment already have a typical high saturation rate and good storage stability. However, the formaldehyde content is often too high for impregnating resin use. In all cases, they can be diluted clear with hot water and at room temperature with at least twenty times the amount of water. After the formaldehyde post-treatment, more urea can be condensed in this without adversely affecting the saturation capacity and storage stability of the resins. The amounts of urea subsequently condensed must be dimensioned so that at the end of the condensation the molar ratio of urea to formaldhyde is 1: 1.5 "1 * 2.2, i.e. it is preferred to add at least 0.2 moles of free urea per mole of condensed urea.

Post-condensation of urea is complete when free urea is bound. In many cases, this occurs after mixing the urea immediately after heating the resin solution or because most often already starting from hot resin solutions. Thus, urea is preferably added in solution, e.g. as an aqueous solution.

It is self-evident that the preparation and post-treatment of the resin with formaldehyde and urea can take place by all known means. It is possible to implement the method in stages and particularly advantageously in a continuous manner, e.g.

5,56541 in tubular reactors, multistage stirred tanks and combination equipment. Depending on the starting solution used and the way in which the formaldehyde and urea are fed, the impregnating resins according to the invention have a dry matter content of about 40 to 60% by weight. Depending on the concentration, they have a viscosity of 15-70 cP. It is most convenient to carry out impregnation with solutions diluted to 40-50% by weight.

The resins can be used as such or in combination with other resins, e.g. melamine or phenolic resins. In this case, the products prepared according to the invention can be mixed in all proportions with other resins.

In addition to pure urea formaldehyde condensates, modified urea formaldehyde condensates can be used to some extent in the described process. Particularly suitable are mixed condensates with a smaller amount of urea, e.g.

20 has been replaced with an equivalent amount of other amino and phenolic resin forming agents, e.g. melamine, phenol and dicyandiamide. The molar ratios mentioned above then apply to the binding capacity of the formaldehyde substitutes calculated from urea, respectively.

The following examples illustrate the invention, with particular reference to the relationship between molar ratios, post-treatment amounts and times. The impregnation time is determined by placing a light gray decorative paper, weighing 100 g / m2, on the surface of the resin solution poured into a flat dish and measuring the time until uniform dark gray. After a little practice, this value can be repeated with an accuracy of less than half a second.

Comparative Test

To describe different methods of measuring the degree of condensation, start with a molar ratio of urea to formaldehyde of e.g. 1: 2.0 and condense in a solution of about $ 50 at boiling temperature. At the beginning of the condensation, the pH is adjusted to 5 * 5 », which drops to 4 * 5 during condensation. After 5 °, more urea is added as a concentrated aqueous solution in a molar ratio of 1: 1.8.

6 56641

Table

Condensation Mg sulfate Water resistance Water resistance duration, min. durability at 20 ° C (1: 5) feamening reaction temperature

(g MgSO 2 .12H90 / ml opx solution) 2 W

0) 10 | (mole- 20) - _ _ (ratio 50 j 1: 2.0 - - 40) 50 45 j 40 5 - 50 + 35 12 - 55) 50 13 - 60 \ mole- 25 18 65 20 20 70 j 15 25 1: 8 milky 75) 10 27 1: 6 precipitate / l: 4 »5 milky ί earthy 6 29 1: 4 precipitate + Urea addition

Example 1

Prepared from a $ 50 aqueous solution of urea formaldehyde condensate, molar ratio of urea to formaldehyde 1: 1.7, pH 4.8, different degrees of condensation in separate individual experiments. The degree of condensation is determined by diluting with eight times the amount of hot water and diluting. In the following table, the notation "20 ° C cloudy" means that when measured with a rod heat meter, the sample diluted in a water bath on cooling begins to cloud at 20 ° C. This measured value can be measured and reproduced with an accuracy of 1-2 ° C. After post-treatment with formaldehyde and urea, the molar ratio of this resin is again 1: 1.7 »7. VCS41 G I tn <U Ό ra w G ··

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9 56541

The table shows that the lower the degree of precondensation of the resin, the less formaldehyde required in the post-treatment for the shortest possible impregnation time.

Furthermore, it is clear from the table that the post-treatment with formaldehyde reduces the viscosity of the resin solution, but at the same time improves the saturation times considerably more (cf. Experiment 1 for Experiments 2 and 3 or Experiment 6 for Experiments 7-11) than would require a change in viscosity. From this it can be concluded that the post-treatment with formaldehyde has not only reduced the degree of condensation, but that it has fundamentally changed the structure of the condensate. In addition, the measured values show that the ratio of urea to formaldehyde during the formaldehyde post-treatment must not fall below 1: 2.5, because with a molar ratio below 1: 2.5 the viscosity no longer decreases as desired, but on the contrary increases and the saturation times deteriorate (cf. experiments 2,3 and 4 to experiment 5 or experiments 10, 11 and 12 to experiment 15). For highly condensed resins, a molar ratio of 1: 2.5-1 s2.7 is hardly sufficient to convert high molecular weight resins to low molecular weight resins (cf. Experiment 15 for Experiments 16 and 17). The method is particularly characterized in that the curing rate does not deteriorate during machining, but clearly improves. This fact is all the more surprising because previous experience has shown that a decrease in viscosity usually meant a slowdown in curing.

Example 2

Condensate by heating at pH 6.0 1829 parts by weight of an aqueous solution of $ 65 urea (molar ratio 1: 1.8) to such an extent that diluting one volume of the resin solution with eight volumes of hot water produces turbidity on cooling to 22 ° C. To the resulting solution is added enough 40 formaldehyde solution that the molar ratio of urea to formaldehyde is 1: 3 * 1 · This mixture is heated to 90 ° C with stirring and maintained at pH 5 * 5 for one hour at this temperature. It is then cooled to 60 [deg.] C. and enough urea is added to the solution that the molar ratio is original, i.e. 1: 1.8. The mixture is kept at pH 5 * 5 for a further 15 minutes at 60 [deg.] C. and then the pH is adjusted to 7.2 to 7.5 with sodium hydroxide solution, dilute to 1.21 g / ml with water and cool to room temperature.

To one hundred parts by weight of the impregnating resin solution thus obtained, 3 parts by weight of an adhesion promoter and 0.03 parts by weight of ammonium chloride are added. This mixture is impregnated with silk cellulose paper, 100 g basis weight. The temperature of the impregnation bath is 20 ° C. Impregnate, based on the weight of the paper, to a resin content of 60 fo. Finally, the impregnated paper is treated in an air recirculation furnace at a temperature of 130-140 ° C. On drying, the evaporation evaporates at a temperature of 135 ° C and a pressure of 8 kp / cm 2 using a conventional urea resin adhesive. A high-quality chipboard with a coating is obtained.

Example 3

Condensing at pH 5 to 5 2000 parts by weight of a $ 60 urea resin solution, molar ratio 1: 2.0, to such an extent that diluting one part of the resin solution with eight parts of hot water results in turbidity on cooling to 30 ° C. Add enough $ 40 formaldehyde solution that the total ratio of urea to formaldehyde is 1: 3 »3 · This mixture is heated to 85 ° C with constant stirring and maintained at this temperature for 75 minutes, maintaining the pH at 5.0. It is then cooled to 60 [deg.] C. and the molar ratio is adjusted to 1: 1.9 by the addition of urea. The resulting clear solution is kept under stirring for 20 minutes at pH 5.2 and 65 ° C, after which it is neutralized with dilute sodium hydroxide solution. Add so much water that the density is 1.20.

700 parts by weight of the urea resin solution thus obtained are mixed with 300 parts by weight of an aqueous solution of $ 50 melamine in which the molar ratio of melamine to formaldehyde is 1: 2. At the same time, 2 more parts by weight of urea resin powder are added, the degree of condensation of which is so high that the resin no longer dissolves but merely swells. In the above solution, the urea resin powder immediately forms a swollen dispersion. This mixture is impregnated with sulphate cellulose paper having a basis weight of 110 g. The impregnating device is adjusted so that the amount of resin absorbed is 115 i ° based on the dry weight of the paper. The impregnated paper is then dried in an air recirculation oven at 145 ° C to remove 5 °. Thus, the so-called a barrier or substrate film which, together with a correspondingly impregnated decorative film, can be processed by means of heat and pressure in a manner known in the manufacture of particle board.

Claims (3)

11 56541 A process for the preparation of storage-resistant urea formaldehyde impregnating resins, in particular for finishing wood surfaces, characterized in that a) urea and formaldehyde are condensed in a known aqueous solution in a molar ratio of 1: 1.5 to 1: 2.5 in a known manner to a cold, 50 to # a sample of the condensate solution dropped into the magnesium sulphate solution causes turbidity and at most to the extent that the resin of the solution remains dissolved above 60 ° C; -1: ¾ and condensed at a temperature between U0 ° C and the boiling point of the solution at pH 3.5 ~ 9 until the resin solution remains clear at room temperature when diluted with at least twenty times the amount of water, and c) then optionally adding urea to a total molar ratio of urea to formaldehyde of 1: 1.5-1: 2.5 and post-condensed at pH U, 0-6.5 free until the disappearance of an urea. Process according to Claim 1, characterized in that a resin which has been condensed at a pH of 1.5 to 6.5 is used in the formaldehyde post-treatment. Process according to Claim 1, characterized in that the post-treatment with formaldehyde is carried out at a pH of k, 5 to 6 x 5. • *. '· T